Do the two pillars on the Golden Gate Bridge appear to be parallel or skewed?

The photograph on the left and right are identical. Therefore, the pillars must be perfectly aligned and parallel. For most people, it appears that the images are skewed. That is, the picture on the right is at a much sharper angle than the picture on the left.

The illusion was discovered by Frederick Kingdom, Ali Yoonessi and Elena Gheorghiu at McGill University. In their version, an image of the Leaning Tower of Pisa was used to demonstrate the effect. As such, this effect is commonly referred to as the “Leaning Tower Illusion”. This discovery won the trio first prize in the Best Visual Illusion of the Year Contest in 2007.